Well, since we are talking about "most useful" I would rather have Gaara's Sand Control. Now you are probably going to bleat "Susanoo is more powerful it has better defence, it is has better offense" - ok I will give you the benefit on the doubt, I WILL say it is more powerful. But since you are talking about "more useful" I'm sticking to Gaara's Sand Control.where did i say it had no drawbacks? name me one technique that is better and reasons y its better and ill agree but until this technique can both defend and attack i wont agree
I will give the reasons of the flaw of the Susanoo
Eyes - Susannoo has great strain on your eyes and can take a great amount of chakra from the User. Also let me add it takes TWO Eyes to activate the Susanoo, now are your term of being "most useful" if both your eyes are strained while using this Ability, then I'm sorry I refuse to call it the "most useful" especially when the User has a huge drawback.
Like I said you can call it "the most powerful" but if strains two of eyes, hurts your vision as we have seen from Sasuke even though he had a incomplete form. Now you cannot relentlessly attack with the Susanoo without those liminations. Is the Susanooo effective and powerful? Yes. Does it hurt the User? Yes as well.
Lets look into another perspective. If Sasuke, Madara, Itachi were in combat battling against thousands of Shinobi and the Susanoo was activated all the time and lets say the battle was going, but the Suaanoo was only in defense mode, by the time they attack, it will impair their vision. They have already lost a ton of Chakra from using the Susanoo. When the Susanoo is on offense mode, they will lose more chakra and it will hurt their eyes. Now this means you cannot attack relentlessy.
Now I will stop and ask you, are you trying talk about most powerful or most useful. To ME, just because something is the most powerful doesn't mean I necessary have it, without considering the drawbacks and to ME I refuse to call the Susanoo the best jutsu or the "most useful" best offense/defense because I simply don't like the disadvantages and I see them more damaging to have rather than have the "ultimate defense"
I'd rather have the Sand Control for various reasons for it's defense or offense. I will explain more, depending on your reply, because frankly I cannot be fu*ked to say more.